Incremental Elevations in TNFα and IL6 in the Human Colon and Procancerous Changes in the Mucosal Transcriptome Accompany Adiposity

A Comprehensive Review of the Triangular Relationship among Diet-Gut Microbiota-Inflammation

The human gastrointestinal tract hosts a complex and dynamic community of microorganisms known as the gut microbiota, which play a pivotal role in numerous physiological processes, including digestion, metabolism, and immune function. Recent research has highlighted the significant impact of diet on the gut microbiota composition and functionality, and the consequential effects on host health. Concurrently, there is growing evidence linking the gut microbiota to inflammation, a key factor in many chronic diseases such as inflammatory bowel disease (IBD), obesity, diabetes, and cardiovascular diseases (CVDs). This review explores how dietary components influence the gut microbiota composition, how these microbial changes affect inflammatory pathways, and the therapeutic implications of modulating this axis for chronic inflammatory disease prevention and management. Beneficial dietary patterns, such as the Mediterranean diet (MD) and plant-based diets, promote a diverse and balanced gut microbiota composition, supporting anti-inflammatory pathways. Conversely, the Western diet (WD), high in saturated fats and refined sugars, is associated with dysbiosis and increased inflammation. With all the links between the three variables considered, this review attempts to offer a thorough examination of the triangle formed by inflammation, the gut microbiota, and food.

Combined Supplementation with Vitamin B-6 and Curcumin is Superior to Either Agent Alone in Suppressing Obesity-Promoted Colorectal Tumorigenesis in Mice

BACKGROUND

Obesity increases the colorectal cancer risk, in part by elevating colonic proinflammatory cytokines. Curcumin (CUR) and supplemental vitamin B-6 each suppress colonic inflammation.

OBJECTIVES

We examined whether the combination of CUR and vitamin B-6 amplifies each supplement's effects and thereby suppress obesity-promoted tumorigenesis.

METHODS

Male Friend Virus B (FVB) mice (4-week-old; n = 110) received 6 weekly injections of azoxymethane beginning 1 week after arrival. Thereafter, they were randomized to receive a low-fat diet (10% energy from fat), a high-fat diet (HFD; 60% energy from fat), a HFD containing 0.2% CUR, a HFD containing supplemental vitamin B-6 (24 mg pyridoxine HCl/kg), or a HFD containing both CUR and supplemental vitamin B-6 (C + B) for 15 weeks. Colonic inflammation, assessed by fecal calprotectin, and tumor metrics were the primary endpoints. The anti-inflammatory efficacy of the combination was also determined in human colonic organoids.

RESULTS

HFD-induced obesity produced a 2.6-fold increase in plasma IL-6 (P < 0.02), a 1.9-fold increase in fecal calprotectin (P < 0.05), and a 2.2-fold increase in tumor multiplicity (P < 0.05). Compared to the HFD group, the C + B combination, but not the individual agents, decreased fecal calprotectin (66%; P < 0.01) and reduced tumor multiplicity and the total tumor burden by 60%-80% (P < 0.03) in an additive fashion. The combination of C + B also significantly downregulated colonic phosphatidylinositol-4,5-bisphosphate 3-kinase, Wnt, and NF-κB signaling by 31%-47% (P < 0.05), effects largely absent with the single agents. Observations that may explain how the 2 agents work additively include a 2.8-fold increased colonic concentration of 3-hydroxyanthranillic acid (P < 0.05) and a 1.3-fold higher colonic concentration of the active coenzymatic form of vitamin B-6 (P < 0.05). In human colonic organoids, micromolar concentrations of CUR, vitamin B-6, and their combination suppressed secreted proinflammatory cytokines by 41%-93% (P < 0.03), demonstrating relevance to humans.

CONCLUSIONS

In this mouse model, C + B is superior to either agent alone in preventing obesity-promoted colorectal carcinogenesis. Augmented suppression of procancerous signaling pathways may be the means by which this augmentation occurs.

Insulin Resistance and Cancer: In Search for a Causal Link

Insulin resistance (IR) is a condition which refers to individuals whose cells and tissues become insensitive to the peptide hormone, insulin. Over the recent years, a wealth of data has made it clear that a synergistic relationship exists between IR, type 2 diabetes mellitus, and cancer. Although the underlying mechanism(s) for this association remain unclear, it is well established that hyperinsulinemia, a hallmark of IR, may play a role in tumorigenesis. On the other hand, IR is strongly associated with visceral adiposity dysfunction and systemic inflammation, two conditions which favor the establishment of a pro-tumorigenic environment. Similarly, epigenetic modifications, such as DNA methylation, histone modifications, and non-coding RNA, in IR states, have been often associated with tumorigenesis in numerous types of human cancer. In addition to these observations, it is also broadly accepted that gut microbiota may play an intriguing role in the development of IR-related diseases, including type 2 diabetes and cancer, whereas potential chemopreventive properties have been attributed to some of the most commonly used antidiabetic medications. Herein we provide a concise overview of the most recent literature in this field and discuss how different but interrelated molecular pathways may impact on tumor development.

Colon Carcinogenesis: The Interplay Between Diet and Gut Microbiota

Colorectal cancer (CRC) incidence increases yearly, and is three to four times higher in developed countries compared to developing countries. The well-known risk factors have been attributed to low physical activity, overweight, obesity, dietary consumption including excessive consumption of red processed meats, alcohol, and low dietary fiber content. There is growing evidence of the interplay between diet and gut microbiota in CRC carcinogenesis. Although there appears to be a direct causal role for gut microbes in the development of CRC in some animal models, the link between diet, gut microbes, and colonic carcinogenesis has been established largely as an association rather than as a cause-and-effect relationship. This is especially true for human studies. As essential dietary factors influence CRC risk, the role of proteins, carbohydrates, fat, and their end products are considered as part of the interplay between diet and gut microbiota. The underlying molecular mechanisms of colon carcinogenesis mediated by gut microbiota are also discussed. Human biological responses such as inflammation, oxidative stress, deoxyribonucleic acid (DNA) damage can all influence dysbiosis and consequently CRC carcinogenesis. Dysbiosis could add to CRC risk by shifting the effect of dietary components toward promoting a colonic neoplasm together with interacting with gut microbiota. It follows that dietary intervention and gut microbiota modulation may play a vital role in reducing CRC risk.

Genetic ablation of tumor necrosis factor-alpha attenuates the promoted colonic Wnt signaling in high fat diet-induced obese mice

Obesity is an established risk factor for colorectal cancer, but the mechanisms responsible for this relationship are not adequately delineated. Using a TNF-α^-/- mouse model, the present study aimed to test the causal role of TNF-α in mediating the promotion of tumorigenic Wnt signaling by high-fat diet-induced obesity. A 2×2 factorial study was performed with wild-type and TNF-α^-/- mice on a 60 kcal% high-fat diet or a 10 kcal% low-fat diet. The inflammatory cytokine profile and genes within the Wnt signaling pathway were measured by electrochemiluminescence assay, real-time PCR, Western blotting or immunohistochemistry. The high-fat diet increased body weights in both wild-type and TNF-α^-/- animals (P<.05), but males were more sensitive to high-fat diet-induced weight gain and increases of colonic TNF-α than females (P<.05). Genetic ablation of TNF-α suppressed the obesity-promoted elevation of Wnt signaling, as indicated by decreased levels of phospho-GSK3β and active β-catenin, two key components within the Wnt pathway (P<.05). The transcriptional expression of several Wnt signaling targets (C-myc, Cyclin D1 and Axin 2) and cell proliferation, as indicated by Ki-67 staining, were attenuated by the deletion of TNF-α in the high-fat-fed TNF-α^-/- animals comparing with the wild-type animals (P<.05). Our data collectively showed that the genetic deletion of TNF-α attenuated the tumorigenic Wnt signaling, which was otherwise elevated by high-fat diet-induced obesity, and demonstrated a causal role of TNF-α in mediating obesity-associated Wnt signaling, which indicates a potential mechanism of inflammation-driven Wnt signaling for obesity-associated colorectal carcinogenesis.